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Parallel Lead Acid Batteries

12VoltInstalls

life passes by too quickly to not live in freedom
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I have seven grp 27 12V batteries in parallel. Not a good layout (sequential) and I want to recable them to a batter arrangement. With seven that’s not really able to be done well either but I’m going to try this arrangement. I just can’t figure a better way it this should be better for the batteries.
I’m also rearranging them to make checking electrolyte level less of a pain by using longer cables that aren’t over the covers.

What do people think of this?
 

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Have you thought about bus bars?
They do have 5/16 studs. But getting the cell covers off to check electrolyte would be more painful.

I’ve also thought of just buying another grp27 and making two equal-length balanced 4-battery banks with a “Y” cable.

I used to just rotate batteries around periodically but after 3 years I’m sick of it and cabling will do the deed once and done.
 
No, I mean instead of all the wires going back and forth between the batteries in a tangle, just getting a couple bus bars and taking each battery to the bus bar individually. Then your cables could all be the same length in whatever length is convenient for cable management and access without having all these bundles criss-crossing across the tops of the batteries.
 

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That would work electrically but I’d need 70’ of new cable!
I think I might add a battery and make two four-battery banks to a buss
 
How many feet of cable is it to do the wire tangle? Also, more batteries is always a good option. :)
I have the existing ~24” cables and I think enough bulk 2ga and terminal ends to do the ‘tangle.’ But to do equal length from buss bars would be too long for any of the existing cables. But I think I have plenty to do a pair 4-bank to a single-stud terminal block (or even a bolt and a thousand rolls of electrical tape LOL).

My biggest thing is I know my current arrangement isn’t good for the lifespan of the batteries and since they’re basically 3 years old I thought if I did them ‘properly’ they could go another few years…
The furnace is like 3.5A but at night the fan essentially never stops due to the ‘purge’ cycle and that constant load is hitting the batteries hard with the short sunlight. Surprisingly burning very little propane - like a gallon maybe per day- but the modern furnace at only 3.5A doesn’t purge like the ancient 12A one did. Plenty of heat but it runs constantly whereas the old one would blast you, be off ‘til it felt chilly, and then blast again. It’s been as low as 11F nights here so that’s cold

My observation is the coffeemaker, fridge, water pump are intermittent and seem to let the batteries ‘recover’ whereas the constant 3.5A draws the volts down more than the math suggests.

So I just want to be kinder to the batteries. It may not help but it won’t hurt.
 
In my signature block, there’s a link for paralleling large batteries. What you’re suggesting seems like a good method. Something like that is listed as an alternate to paralleling batteries with the busbar method. I never realized how much extra cable that would go through.

Someday I’d like to test amps drawn to see if the draw is as extreme in improperly cabled batteries as the document suggests. A clamp meter would easily do that, I just don’t have the number of batteries for that.

My biggest load is also the propane blower motor. Mine is 9 amps on my RV. The microwave pulls 155 amps if I turn it on, but the blower constant usage on a cold night adds up compared to only 8 minutes a day for the microwave.
 
Someday I’d like to test amps drawn to see if the draw is as extreme in improperly cabled batteries as the document suggests.
I think I’ve read that doc before.

I’ve seen other dissertations on parallel and batteries. For parallel one source (can’t remember where) suggested - not even considering potential battery damage - that long parallel battery runs can suppress storage across the batteries as much as 30% effective use with lead acid batteries.

This is my first winter that other than occasional weekends I’ve actually lived in the RV. The furnace is new (the old one had too many jerry-rigged stuff from previous owner and I wasn’t willing to actually spend or depend on it). Summertime I’ve got plenty of solar and batteries even for several cloudy days. Winter I’m using 100% every night. 12.1V right now, and cloudy.

A better battery bank layout makes sense and IF it gives me 30%…that’s great!

I’m actually enjoying this experiment/experience. I started this- approach- 3+ years ago when I was working but “poor” and just wanted to save some money. I almost had to sacrifice to change my circumstances. Today: I do have more than enough money to live on, money in savings, and I am choosing to do this as anything less money than traditional rent is savings. And it’s a fun experiment again. I’m about to go 100W 4S2P from my current 3S2P and I can’t wait to see what that does during this ‘dark season.’
 
Do you have a clamp meter you can test your current set of batteries with? For your battery, if you can measure amps during a larger load, and you see a difference, then cabling could be in order, but if there is no measurable difference then cabling might not be called for. The math probably says it should, but there could be some things that make that link more skewed to show a big difference that does not apply in your case.

The link does give some values for resistance, but the difference between 2/0 and 6 AWG would be huge, enough so IMO that at 6 AWG if the differences were huge, they may disappear at 2/0. Also, in my very limited attempts at measuring battery resistance using a cheap Battery Discharge tester, DL-24P, the battery resistance when full is quite a bit lower when it starts and gradually increased to many times what it was when started versus empty.

That would skew the numbers in the link by quite a bit.

I did some playing around with another link in my signature block this weekend, Mixing and Matching Solar Panels. When Panels in different parallel string have different voltages, the total of all strings is supposed to take the lowest voltage. To my surprise, with 35 VDC, 42 VDC, and 66 VDC for each string I was expecting the voltage once combined to be 35 volts, but the total voltage was 55 volts. Also, the math said I should be losing power by a lot, but the total wattage was nearly the sum of the three panels.

Sometimes there’s things that make the math not add up like it should, perhaps for my solar panels it was an MPPT controller In the mix, or could be somethign else altogether.
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I think what you’re doing is pretty exciting and I would love to move into the RV, but my wife won’t agree to that. Enjoy!!
 
The furnace is like 3.5A but at night the fan essentially never stops due to the ‘purge’ cycle and that constant load is hitting the batteries hard with the short sunlight. Surprisingly burning very little propane - like a gallon maybe per day- but the modern furnace at only 3.5A doesn’t purge like the ancient 12A one did. Plenty of heat but it runs constantly whereas the old one would blast you, be off ‘til it felt chilly, and then blast again. It’s been as low as 11F nights here so that’s cold
Man I wish mine did that. I replaced my old furnace when it died with a brand new Suburban unit and I hate it. It sucks the power like crazy, runs for almost a minute, blows air for 5 minutes, runs for a minute, repeat. It never gets the place warm but it will eat 2 40lb propane tanks in a week.

I went to two of the chinese diesel heaters and some ductwork and those work SSSSOOOO much better. Yes, I have to have another fuel at the camp (diesel) but I only burn about 10gal a week total when we get highs in the teens Fahrenheit. Add the only couple of amps of 12v draw per hour between the two and it's just better in pretty much every way.

Fortunately when I re-do my solar (if/when I can ever get back there) my battery shelf is only a couple feet from where all the inverter/SCC/transformers/etc are mounted that I'll be able to just connect them all straight to the bus bars rather than trying to do a 6-battery tangle.
 
the math said I should be losing power by a lot, but the total wattage was nearly the sum of the three panels.
Sometimes there’s things that make the math not add up like it should

There are several things like that which show up occasionally where the math doesn’t work.

I do have a clamp meter. Just barely received a Klein last week. I never even thought while I was making (600W) coffee to go out and check. I did verify the furnace at 3+ amps because it “felt” like 10A. But no, 3-3.5A depending on part of cycle. Which is why I started thinking about my battery layout again… in theory I have plenty of battery…

A thing that doesn’t (initially) make sense: Last year when I was still pwm and I put two 100W panels in series. I got (minimal) panel output of an amp or two or three whereas the panels in parallel weren’t (on that cloudy day) making more than battery voltage. The series panels did to my surprise. Granted I didn't ever get more than ~5A cuz with series on a pwm it was essentially one panel but I got some charge earlier and more often if no sunshine this time last year. It didn’t matter cuz I wasn’t here often but it would be charged up to make coffee and have lights when I was here!

wish mine did that. I replaced my old furnace when it died with a brand new Suburban unit and I hate it. It sucks the power like crazy, runs for almost a minute, blows air for 5 minutes, runs for a minute, repeat. It never gets the place warm but it will eat 2 40lb propane tanks in a week.
I bought a 16K BTU suburban
I’m only like a gallon or less /day, but the forever fan with interspersed short runs of the flame is what mine does, too. I’m about R11-R12 for some areas. I need to pull the floor and put foam in after replacing two floor joists below where previous owner didn’t fix a leaky skylight and it ran into that corner with predictable results. Plus the skylight no longer exists…

By the end of the winter or the next few weeks maybe? the camper will be fully foam insulated and plexi ’storm’ panels for the windows. Staying here this winter was a last minute impulse when I was nearing writing a check for $2500 to rent an apartment. I balked and went on a spending spree to increase solar and insulate. Considering I’ve still got 40+ square feet of single glass windows and only half the walls and ceilings insulation upgraded I’m doing ok!
 
never realized how much extra cable that would go through.
8 batteries would need 16 lengths at ~54”
Someday I’d like to test amps drawn to see if the draw is as extreme in improperly cabled batteries as the document suggests. A clamp meter would easily do that, I just don’t have the number of batteries for that.
I should have written it down. On the sunny day last week I used the clamp meter and ya, the middle of the bank was less amps than those at the SCC connection points.

It got dark too fast with the money thick clouds for me to finish my upgrade project today. But I have some cables made up and the 2/0 battery cable terminal ends crimped; and ‘rotated’ the batteries.

I’ve only got one string (4S) plugged in right now because I need to remove the 8ga and install the new 6ga. The output of everything could be 88-106Volts and +40A so…

I should be able to go live tomorrow with the 800W
 
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